A digital versatile disc (DVD) which is the mainstream standard of optical discs and enables high-density recording has a structure constituted by two 0.6-mm-thick substrates bonded to each other with an adhesive. In order to achieve higher densities in DVDs, a 650 nm laser beam having a wavelength shorter than that used for compact discs (CDs) has been used and the numerical aperture of the optical system has been increased.
However, higher densities are needed to read and record high-quality images suitable for high-definition televisions (HDTV). Studies are being made on methods for achieving even higher recording densities, which will mark the next generation of DVDs, and optical discs for such use. There has been proposed a high-density recording method in which a novel optical disc structure is employed that uses a blue laser beam having a wavelength shorter than that used for DVDs and an optical system having a high numerical aperture.
This optical disc is obtained by forming a recording layer on a transparent or opaque substrate composed of a plastic such as polycarbonate and stacking a light-transmitting layer about that is 100 μm in thickness on the recording layer and is configured to allow entry thereinto of recording light and/or reading light through the light-transmitting layer. From the viewpoint of productivity, most studies have focused on the use of UV-curable compositions in the light-transmitting layer of an optical disc.
Optical discs are required to retain stable read-write characteristics on a long-term basis. Thus, the light-transmitting layer preferably has high shape stability. When the light-transmitting layer constitutes the outermost layer, surface properties of being resistant to scratching and adherence of fingerprints and the like and allowing fingerprints to be easily wiped off are desirable. A composition that contains inorganic particles such as silica, a silane compound, etc., and that improves the slidability of the surface has been disclosed as a composition to be used in the outermost layer of an optical disc (e.g., refer to PTL 1 and PTL 2). However, when a composition containing fine inorganic particles or a silane compound is used in a thick light-transmitting layer that serves as the outermost layer of an optical disc, the compatibility is poor and cloudiness may occur.
A UV-curable composition containing a silane compound has been disclosed as a UV-curable resin composition that resists adherence of contaminants such as fingerprints (e.g., refer to PTL 3). Although this UV-curable composition can properly prevent adherence of fingerprints, when the composition is used at a surface of a light-transmitting layer of recordable blu-ray discs such as BD-R and BD-RE discs and read/write operation is conducted after adherence of fingerprints, sufficient and satisfactory signal characteristics are not always achieved due to the large droplet size of the fingerprints.